Hi lowpoint
I am sorry that you went through what you did with your father

But, I'd say that
this: "......She almost worships me to the point of annoyance........" says much, much more than you credit it for

To me, this says that you
weren't the sort of brother you seem to be perceiving yourself as..........and naturally abuse (the kind of abuse you went through!!!) can distort your thinking about yourself, have you seeing yourself in the most negative light...........but I seriously doubt that your sister saw you that way
And some self compassion, hey??!!
It might be easier to look back now and think "Why didn't I say.........to her............do..........for her" but........
you were being abused. Sometimes you don't even know what to say to yourself to make things a little better, let alone to someone else.........sometimes you just want/need to pretend that it isn't so bad...........sometimes you feel you just have to accept what is going on...........sometimes you feel you just need to be away from anyone/everyone..........sometimes you've barely got enough emotional strength for yourself nevermind others............right??
And those things can be the case after the abuse has ended too..........
So just as the abuse wasn't your fault, so is the fact you weren't able to do more for your sister
And now.........well I'd say that it's
great that you want to be there for her, so try not to let anything,
including guilt you don't deserve, stand in the way of that, hey??!!
Alison